Acidic metal salt solutions, such as aluminum sulfate ((Al.sub.2 (SO.sub.4).sub.3.14H.sub.2 O) solution, have long been employed to remove turbidity, color and suspended particles, as well as organic and microbiological contaminants, from surface waters. Surface waters as employed herein include municipal water supplies, river water, lake waters, reservoirs and the like. Aluminum sulfate, or alum, is readily available, either as a solid or as a strongly acidic 48.5% by weight solution. When it is diluted with surface water, it can function as a coagulant, flocculent, precipitant and emulsion breaker. As a coagulant, alum removes algae in the water; algae take up and thus remove oxygen from the water (known as biochemical oxygen demand or BOD) and thus pose a danger to fish. It forms an insoluble precipitate or floccule, i.e., a floc, from impurities in the water. The floc grows in size as it attracts suspended and colloidal particles and organic compounds present in the water. The floc settles out of the water over time and can then be removed, as by decanting or filtering the water.
Various additives in combination with the acidic metal salt solution that aid in the removal of contaminants present in water are known, including the addition to the acidic metal salt of various organic polymers, and inorganic materials such as calcium chloride, activated carbon, silicates, phosphates, sodium hydroxide and the like. One prior art mixture of this kind is disclosed in U.S. Pat. No. 4,076,615 to Olesen et al.
Recently the United States government and various state and local agencies have increased their requirements for water purity, particularly with respect to removal of organic materials. Thus more restrictions have been placed on the organic content of drinking water and waste waters, and federal and state regulations are expected to require very low levels of organic material. In many situations it may be expected that the current and prior art water treatments and current practices, as more stringent limits are legislated, may be unable to meet the new requirements and higher standards for water purity economically.
Thus there is an important need for an improved means of removing contaminants from water so as to comply with anticipated more rigorous requirements for clean water.